Hydrogen Sulfide in Water

A dissolved gas with a distinctive rotten-egg odor.

If your water smells like rotten eggs, hydrogen sulfide is almost certainly why. The good news: at the levels found in household water it’s a nuisance, not a health hazard — unpleasant, corrosive to plumbing over time, and very fixable once you know where it’s coming from.

What it is

Hydrogen sulfide is a gas produced by sulfur bacteria and natural chemical reactions underground. Even tiny concentrations are detectable by smell — your nose is more sensitive to it than most tests — which is why the odor usually arrives before any other sign.

How it gets into water

Sulfur bacteria in wells, plumbing, or water heaters are the usual culprits. A useful home diagnostic: if only hot water smells, the water heater’s anode rod is likely the source; if both hot and cold smell, the well or supply is.

What a result can tell you

There’s no formal EPA limit — the marker’s value is confirmation and severity. A positive result verifies the odor is sulfide rather than something else, and helps you choose the fix: replacing a water heater anode, shock-chlorinating a well, or installing aeration or oxidizing filtration for persistent cases.

What it can’t tell you

The strip can’t tell you which part of the system harbors the source — the hot-versus-cold comparison and a well inspection do that. And because sulfide corrodes metals, a long-standing odor problem is worth solving for your plumbing’s sake even though your health isn’t at stake.